Hippocampus and Spatial Memory in Brood Parasitic Cowbirds

Abstract

Natural selection can modify cognition and its neural mechanisms if these modifications enhance fitness. Brood parasites are ideal subjects to study sex-specific adaptations in cognition and the brain because it is often females that search for potential host nests, and some species as a result show a reversal of sex-typical space use usually seen in mammals. Research from North and South America shows that female brown-headed (Molothrus ater) and shiny (M. bonariensis) cowbirds have a larger hippocampus than males, and female brown-headed cowbirds exhibit more hippocampal neurogenesis than males. Female cowbirds have better spatial memory than males in some tasks, especially tasks requiring long-term spatial memory in an ecologically relevant context. The hippocampus and spatial memory in cowbirds appear to be specialized for brood parasitism. Because of their diversity and unusual breeding biology, brood parasites offer many opportunities for investigating general questions about the adaptive modification of cognition and the brain.